Here is my hydrometer reading of distilled water at 68F (my hydrometer is calibrated to 68F (

And my hydrometer reading the same water immediately after dissolving about 4 grams of Fleishman dry pizza yeast. (Half the packet)

And my hydrometer reading the same water after dissolving another 4 grams into it, total of 8.

There is no sugar, there is no gas being produced. The time involved was about 3 minutes start to finish, once I got my water to exactly 68F. You can see a tiny bit of foam at the top, that's from me shaking it to mix. Naked eye in person, it was all in the top 1/4". Much like taking an FG reading of green beer that still has yeast in suspension. I don't think it's enough to lift the hydrometer 10 points

I highly doubt there is sugar in Fleishman pizza yeast, but I thought that might be an argument. Interesting coincidence, if the entire 8 grams was pure cane sugar my recipe calculator says it should be 1.010 gravity. Goofy coincidence. Unless someone can prove otherwise, I am assuming they don't add 8 grams of sugar to their package of 8 grams of dehydrated yeast.

Anything that dissolved will increase the density of the water and raise the specific gravity - not just sugars but also salts. Dried yeasts contain a lot if soluble minerals so they might have an effect if you add a lot if yeast to a small sample of water.

I didn't take photos, but did two tests (4g and 8g instant dry bread yeast in 200ml water) and took both hydrometer and refractometer readings, or tried! It looks like each increment of yeast added ~0.006 to the hydrometer reading. The refractometer might seem to agree, but while the hydrometer was impossible to read correctly through the cloudy sample (mine read at the bottom of the meniscus), the refractometer showed no bright line at all, just a fuzzy gradation of shading. I have never read a wort or beer sample anywhere near, by orders of magnitude, this cloudy, nor can I imagine I ever will. So is this something that is not significant under real brewing conditions?

Dry yeast by nature contains its own glycogen reserves. It's like a natural sugar. Rehydration no doubt brings out some of these sugars.

Also the manufacturer possibly adds sugar to kickstart the process, maybe.

The yeast I used, standard commercial baking yeast, is just yeast and ascorbic acid, made by LeSaffre by the same process they use for dry beer yeasts. At least that's what they disclose. As active yeast, there are glycogen reserves, but apparently no added sugars.

On this thread, just for kicks, let's try to prove our assumptions, or disprove them. So far all I am saying is that suspended solids (yeast) effect a hydrometer reading. It appears that the amount of effect is in relationship to the amount of suspended solids.

Where I'm headed with this. Is using a hydrometer really the benchmark when determining final gravity in a finishing/finished beer? Is it reliably more accurate than the average correction factor / refractometer software/spreadsheet/Apps?

My hypothesis would be: 1) of course anything but water in water makes it denser 2) any instrument that measures density will, with proper use, reflect that equally well (no preferred instrument) and 3) at the point you are taking FG readings there will be so little suspended yeast left, that it will be an insignificant contributor to the density of the sample, far smaller than the margin of error in just reading the instrument (unless that instrument costs as much as your house and is in a university lab.)

A method that might throw light on this is to take a FG sample and measure it, then refrigerate it for a few days to settle any yeast and read again. The problem I see with this is the possibility of continued fermentation. I may not be able to contribute much there, because a) I take my sample after crash cooling anyway and b) I know my yeast (34/70) will in fact keep fermenting after crashing.

But hopefully you'll get enough citizen brewing scientists going here to get a real answer! As OP you are the official proctor. Good luck.

I think we need to re-design the experiment to use cruddy old spent yeast, rather than fresh dried yeast.

And... it so happens that I currently have a LOT of old yeast, about 1.5 quarts of it, from a batch I just racked off last night and did NOT package the yeast yet. It's still in the carboy, ready for experiments. Mua ha ha ha ha!!

I'm thinking, my quick test suggests that 0.001 sg requires about 0.003 g/1ml of yeast (sorry Dave I know, fresh yeast but) which by my estimate is ~37.5 million cells/1ml. That's a boatload of yeast. Not what you'd have under real conditions. I'm sure I've made some error, but it's illustrative. Yes Dave, on to the experiments!

My hypothesis would be: 1) of course anything but water in water makes it denser 2) any instrument that measures density will, with proper use, reflect that equally well (no preferred instrument) and 3) at the point you are taking FG readings there will be so little suspended yeast left, that it will be an insignificant contributor to the density of the sample, far smaller than the margin of error in just reading the instrument (unless that instrument costs as much as your house and is in a university lab.)

A method that might throw light on this is to take a FG sample and measure it, then refrigerate it for a few days to settle any yeast and read again. The problem I see with this is the possibility of continued fermentation. I may not be able to contribute much there, because a) I take my sample after crash cooling anyway and b) I know my yeast (34/70) will in fact keep fermenting after crashing.

But hopefully you'll get enough citizen brewing scientists going here to get a real answer! As OP you are the official proctor. Good luck.

Your making assumptions. I could do that too. But it's not proving or disproving anything. How do we know that our green hazy beer does not have enough suspended solids, regardless if it's yeast, protein, starch, hop polyphenols, to effect our hydrometer reading? What instrument or calculus are we using to determine that?

I think we need to re-design the experiment to use cruddy old spent yeast, rather than fresh dried yeast.

And... it so happens that I currently have a LOT of old yeast, about 1.5 quarts of it, from a batch I just racked off last night and did NOT package the yeast yet. It's still in the carboy, ready for experiments. Mua ha ha ha ha!!

You could filter the yeast suspension through a coffee filter. Dissolved carbohydrates and salts will pass through, suspended particles won't. Then take gravity of the filtrate. I'm 99% sure it will be higher than distilled water.

You could filter the yeast suspension through a coffee filter. Dissolved carbohydrates and salts will pass through, suspended particles won't. Then take gravity of the filtrate. I'm 99% sure it will be higher than distilled water.

Go for it. But also measure it as is. So just water, water with yeast, then that water minus yeast. Probably don't even need to filter, just let it settle to the bottom. Will there be a difference between in suspension and settled out? I suspect yes.

My hypothesis would be: 1) of course anything but water in water makes it denser 2) any instrument that measures density will, with proper use, reflect that equally well (no preferred instrument) and 3) at the point you are taking FG readings there will be so little suspended yeast left, that it will be an insignificant contributor to the density of the sample, far smaller than the margin of error in just reading the instrument (unless that instrument costs as much as your house and is in a university lab.)

A method that might throw light on this is to take a FG sample and measure it, then refrigerate it for a few days to settle any yeast and read again. The problem I see with this is the possibility of continued fermentation. I may not be able to contribute much there, because a) I take my sample after crash cooling anyway and b) I know my yeast (34/70) will in fact keep fermenting after crashing.

But hopefully you'll get enough citizen brewing scientists going here to get a real answer! As OP you are the official proctor. Good luck.

Your making assumptions. I could do that too. But it's not proving or disproving anything. How do we know that our green hazy beer does not have enough suspended solids, regardless if it's yeast, protein, starch, hop polyphenols, to effect our hydrometer reading? What instrument or calculus are we using to determine that?

I said it's a hypothesis, that's my point, it needs to be tested. Somehow we need to see what yeast all by itself does, because we expect all that other stuff to be in there too. (And in the end, if you know that x APPARENT attenuation means it's time to rack, does it matter what all the floaties are, or the REAL attenuation?) Still this will be good to know. Everything's good to know! Looking forward to it.

You could filter the yeast suspension through a coffee filter. Dissolved carbohydrates and salts will pass through, suspended particles won't. Then take gravity of the filtrate. I'm 99% sure it will be higher than distilled water.

pretty much what I did after cold crashing for a few days. I took a cloudy post boil sample with a lot of suspended "gunk" and measured it. I chilled it for 2-3 days, filtered it, them measured it again.

Here's water 1.000 compared to water with a half tsp of white flour suspended 1.004. I'll let it settle out and check again. I'm doubtful that 1 min in 68F water is enough to convert flour to sugar.(https://uploads.tapatalk-cdn.com/20180209/c6861ef52c21d66d478246ede4ffb662.jpg)(https://uploads.tapatalk-cdn.com/20180209/44f233aa569d16152eac08fbdddd0b73.jpg)

Let's go with the poodles thought experiment. The principle of flotation says that an object afloat will displace a volume of liquid with weight equal to the weight of the object. Note that it is only the liquid displaced by the floating object that matters, not the average density of the contents of the container. If you have rocks or flocculated yeast at the bottom of your container they will affect the weight-to-volume ratio of the container as a whole but if the float does not go low enough to touch the rocks or yeast, then only the density of the liquid on top matters.

Now to the poodles. If you have a bunch of normal-sized poodles in a swimming pool and you drop a normal-sized hydrometer float in between them, your reading will be the same as if the poodles aren't there because they aren't being displaced significantly by your float. If you drop your float right on top of a poodle it will not sink at all, and your reading will be grossly affected (giving a very high density reading). Now imagine the poodle getting smaller and smaller until the weight of the float is comparable to the weight of the poodle. Now the extra weight on top of the poodle will begin to push it down in the water and your float will sink a bit, giving intermediate readings. Now imagine that you have billions of microscopic poodles per liter of water and you drop your float on top of them. It will displace many poodles along with the water, and give a reading that reflects the density of (poodle weight in displaced volume + water weight in displaced volume)/displaced volume. Assuming that the poodles are denser than water (my experience is that some poodles are denser than others) then the density reading will go up as more poodles are added per liter. That is the case for yeast. For real microscopic poodles (??), which were assumed to be floating at the start, their density is less than water so a lower reading would be obtained.

Jim's experiment is consistent with this. When he had flour particles in suspension, they were displaced by his float and raised the reading. After the all sank to the bottom they were no longer displaced by his float and his reading was back to that of water.

• A chilled and settled sample will then give a more accurate reading than a sample straight from the fermentor. But I still want to know, how much suspended yeast (population of poodles) is needed before it causes an error more significant than other factors?

•What does yeast do to a refractometer FG reading, or can we assume (as I do) that this is baked into the cake of refractometer calculators? (OP's OQ before moving the thread was what instrument is most reliable for FG.)

• A chilled and settled sample will then give a more accurate reading than a sample straight from the fermentor. But I still want to know, how much suspended yeast is needed before it causes an error more significant than other factors?

•What does yeast do to a refractometer FG reading, or can we assume (as I do) that this is baked into the cake of refractometer calculators? (OP's OQ was what instrument is most reliable for FG.)

I think you have to keep in mind, when wondering how it's baked into the cake, is we usually take our OG readings before pitching the yeast. No?

Let's go with the poodles thought experiment. The principle of flotation says that an object afloat will displace a volume of liquid with weight equal to the weight of the object. Note that it is only the liquid displaced by the floating object that matters, not the average density of the contents of the container. If you have rocks or flocculated yeast at the bottom of your container they will affect the weight-to-volume ratio of the container as a whole but if the float does not go low enough to touch the rocks or yeast, then only the density of the liquid on top matters.

Now to the poodles. If you have a bunch of normal-sized poodles in a swimming pool and you drop a normal-sized hydrometer float in between them, your reading will be the same as if the poodles aren't there because they aren't being displaced significantly by your float. If you drop your float right on top of a poodle it will not sink at all, and your reading will be grossly affected (giving a very high density reading). Now imagine the poodle getting smaller and smaller until the weight of the float is comparable to the weight of the poodle. Now the extra weight on top of the poodle will begin to push it down in the water and your float will sink a bit, giving intermediate readings. Now imagine that you have billions of microscopic poodles per liter of water and you drop your float on top of them. It will displace many poodles along with the water, and give a reading that reflects the density of (poodle weight in displaced volume + water weight in displaced volume)/displaced volume. Assuming that the poodles are denser than water (my experience is that some poodles are denser than others) then the density reading will go up as more poodles are added per liter. That is the case for yeast. For real microscopic poodles (??), which were assumed to be floating at the start, their density is less than water so a lower reading would be obtained.

Jim's experiment is consistent with this. When he had flour particles in suspension, they were displaced by his float and raised the reading. After the all sank to the bottom they were no longer displaced by his float and his reading was back to that of water.

We need a volunteer. Who has a poodle they can set their hydrometer on and see what the reading is?

• A chilled and settled sample will then give a more accurate reading than a sample straight from the fermentor. But I still want to know, how much suspended yeast is needed before it causes an error more significant than other factors?

•What does yeast do to a refractometer FG reading, or can we assume (as I do) that this is baked into the cake of refractometer calculators? (OP's OQ was what instrument is most reliable for FG.)

I think you have to keep in mind, when wondering how it's baked into the cake, is we usually take our OG readings before pitching the yeast. No?

This question originated on another thread, where the question was about whether yeast really causes huge errors, as claimed by Palmer, and whether hydrometer or refractometer would be more accurate for FG. This question interests me most, because I think we understand pretty well how to choose a measurement method for wort.

• A chilled and settled sample will then give a more accurate reading than a sample straight from the fermentor. But I still want to know, how much suspended yeast (population of poodles) is needed before it causes an error more significant than other factors?

•What does yeast do to a refractometer FG reading, or can we assume (as I do) that this is baked into the cake of refractometer calculators? (OP's OQ before moving the thread was what instrument is most reliable for FG.)

I'm assuming suspended solids will diffuse light, not refract it. Meaning solids do change the degree of but at some point would diffuse it to the point that it's difficult to tell exactly where the line is.

A 2ml sample should be easier to settle than a 200ml sample, and reheat to proper measuring temp.

But the outcome of this thread is up to the reader. I was just curious if it was true that suspended solids effect hydrometers. And it's quite obvious to me that they do.

Gotcha. But if we're measuring attentuation, don't we need to level the field between OG and FG?

I think you're inching toward another question I raised: IS anybody actually measuring attenuation? Or do we just look for an APPARENT attenuation that cues us to move to the next stage of fermentation or cellaring? In which case, consistency matters, accuracy doesn't. But that is really separate from OP Jim's query.

You could filter the yeast suspension through a coffee filter. Dissolved carbohydrates and salts will pass through, suspended particles won't. Then take gravity of the filtrate. I'm 99% sure it will be higher than distilled water.

Go for it. But also measure it as is. So just water, water with yeast, then that water minus yeast. Probably don't even need to filter, just let it settle to the bottom. Will there be a difference between in suspension and settled out? I suspect yes.

I don't have a hydrometer any more - gave it to my sister-in-law's nephew. Only a refractometer.

I don't think the suspended matter would affect a refractometer in the same way. The refractometer is measuring how much light is refracted when it enters a transparent medium that's more dense than air. Suspended matter makes the liquid non-transparent and screws up the reading. You can only get a valid reading by removing the gunk.

Refractometers are calibrated to read correctly for water with a simple content of sugar. We need wort correction factors because wort has many sugars and other things that the refractometer was not designed to measure. Same for alcohol, so we need to correct refractometer readings after fermentation has started. If you add yeast to the solution you will need to correct for it because it isn't the sugar the refractometer was calibrated with. I don't know if the typical quantity of yeast per volume is enough to change the reading significantly, but I do know that cloudy liquids scatter the light in a refractometer and give very fuzzy lines which make it hard to get a decent reading.

You could filter the yeast suspension through a coffee filter. Dissolved carbohydrates and salts will pass through, suspended particles won't. Then take gravity of the filtrate. I'm 99% sure it will be higher than distilled water.

Go for it. But also measure it as is. So just water, water with yeast, then that water minus yeast. Probably don't even need to filter, just let it settle to the bottom. Will there be a difference between in suspension and settled out? I suspect yes.

I don't have a hydrometer any more - gave it to my sister-in-law's nephew. Only a refractometer.

I don't think the suspended matter would affect a refractometer in the same way. The refractometer is measuring how much light is refracted when it enters a transparent medium that's more dense than air. Suspended matter makes the liquid non-transparent and screws up the reading. You can only get a valid reading by removing the gunk.

Let's go with the poodles thought experiment. The principle of flotation says that an object afloat will displace a volume of liquid with weight equal to the weight of the object. Note that it is only the liquid displaced by the floating object that matters, not the average density of the contents of the container. If you have rocks or flocculated yeast at the bottom of your container they will affect the weight-to-volume ratio of the container as a whole but if the float does not go low enough to touch the rocks or yeast, then only the density of the liquid on top matters.

Now to the poodles. If you have a bunch of normal-sized poodles in a swimming pool and you drop a normal-sized hydrometer float in between them, your reading will be the same as if the poodles aren't there because they aren't being displaced significantly by your float. If you drop your float right on top of a poodle it will not sink at all, and your reading will be grossly affected (giving a very high density reading). Now imagine the poodle getting smaller and smaller until the weight of the float is comparable to the weight of the poodle. Now the extra weight on top of the poodle will begin to push it down in the water and your float will sink a bit, giving intermediate readings. Now imagine that you have billions of microscopic poodles per liter of water and you drop your float on top of them. It will displace many poodles along with the water, and give a reading that reflects the density of (poodle weight in displaced volume + water weight in displaced volume)/displaced volume. Assuming that the poodles are denser than water (my experience is that some poodles are denser than others) then the density reading will go up as more poodles are added per liter. That is the case for yeast. For real microscopic poodles (??), which were assumed to be floating at the start, their density is less than water so a lower reading would be obtained.

Jim's experiment is consistent with this. When he had flour particles in suspension, they were displaced by his float and raised the reading. After the all sank to the bottom they were no longer displaced by his float and his reading was back to that of water.

Seems logical to me. Another way to think of it is imagine taking the gravity of thick porridge, runnier porridge, even runnier...

So suspended yeast might inflate gravity readings, but in a beer that's attenuated the yeast will drop out as sugar disappears, so it shouldn't be a big problem.

Adding anything to water will change the density. Think about quicksand. The sand isn't dissolved in water, but the density is such that you can "float" on top of it easily.

Or antifreeze in your car. Or nitrogen bubbles in a freshly poured Guinness. (I've been recently schooled by the latter recently)

Back to the antifreeze, that brought to mind a specific point: Gravity is NOT a measure of sugar content, it's a measure of density. As in any Engineering problem, you have to keep the units straight...

Gravity is density, not sugar content, BUT: The Plato scale is an expression of density based on percent sugar in solution, and refractometers are calibrated to measure an analogous scale, calibrated to refractivity of a pure sugar solution. So in actual brewing practice, you have to account for the fact that you are not in fact dealing with a pure sugar solution, even though that's what all your measuring systems assume. (Assume. You know, as in "Assume a spherical cow....")

How long did that take? There's a lot of flour at the bottom, so another hypothesis is that enough flour temporarily provides nucleation points for rising dissolved gasses and due to surface tension lifts the refractometer. Any ideas how to test this?

Also, ascorbic acid which is in dry yeast as an antioxidant is soluble in water and is a derivative of glucose. How much is in there, I don't know.

How long did that take? There's a lot of flour at the bottom, so another hypothesis is that enough flour temporarily provides nucleation points for rising dissolved gasses and due to surface tension lifts the refractometer. Any ideas how to test this?

Also, ascorbic acid which is in dry yeast as an antioxidant is soluble in water and is a derivative of glucose. How much is in there, I don't know.

I have conducted the flour experiment. Water read 1.001. Water plus a lot of flour read 1.012. After waiting 15 minutes, water plus settled flour read 1.004.

So yeah. Suspended solids can change the gravity. Some of the poodles are holding up the hydrometer... for a little while. Once settled out, they don't anymore.

I could repeat the experiment with yeast, but I'm sure I'd get the same results.

What does this matter? Well... if your beer is as murky as a juicy fresh NEIPA, it might matter. Also if you're measuring gravity in early primary fermentation stage, it might not be so accurate. But any other fully fermented beer style...... no impact at all, I don't think. Maybe 0.001. But not enough to matter. My 1.004 flour stuff settled for 15 minutes was still fairly murky, and that was only 0.003 higher than expected (subtracting 1.001 for the reading in plain water). So.

People can believe whatever they want. In my brewery, suspended solids effect the hydrometer reading.

It's not that I don't believe you. Just trying to figure out how much these tests relate to actual brewing conditions.

How does a fresh sample from the fermenter compare to a sample that has crash cooled for 24 hours?

Simple way to know. Measure both.

I was unaware that suspended solids did this. Then last week I heard Palmer say that he was working on figuring out NE IPAs. He tested water with starch in suspension and it read 1.010, but 1.000 after it settled to the bottom.

Sometimes I take readings during fermentation to determine rate of fermentation, and ADF to determine when to increase temp. Those samples can be quite full of suspended solids. So the hydrometer reading can't be relied on. I'm finding that a better method is to pull a tiny sample, which chills and settled faster, and take a refractometer reading and use a calculator to adjust for alcohol.

People can believe whatever they want. In my brewery, suspended solids effect the hydrometer reading.

It's not that I don't believe you. Just trying to figure out how much these tests relate to actual brewing conditions.

How does a fresh sample from the fermenter compare to a sample that has crash cooled for 24 hours?

Simple way to know. Measure both.

I was unaware that suspended solids did this. Then last week I heard Palmer say that he was working on figuring out NE IPAs. He tested water with starch in suspension and it read 1.010, but 1.000 after it settled to the bottom.

Sometimes I take readings during fermentation to determine rate of fermentation, and ADF to determine when to increase temp. Those samples can be quite full of suspended solids. So the hydrometer reading can't be relied on. I'm finding that a better method is to pull a tiny sample, which chills and settled faster, and take a refractometer reading and use a calculator to adjust for alcohol.

Suspended solids of large size fall out pretty quickly, though. I'm more interested in the effect of something that can stay in suspension after 24 hours of chilling.

EDIT: I can see how this might affect fermenting beer, where yeast tends to stay in suspension. Although I'm already 100% on the refractometer train for that since it's so much easier to take a sample.

People can believe whatever they want. In my brewery, suspended solids effect the hydrometer reading.

It's not that I don't believe you. Just trying to figure out how much these tests relate to actual brewing conditions.

How does a fresh sample from the fermenter compare to a sample that has crash cooled for 24 hours?

Simple way to know. Measure both.

I was unaware that suspended solids did this. Then last week I heard Palmer say that he was working on figuring out NE IPAs. He tested water with starch in suspension and it read 1.010, but 1.000 after it settled to the bottom.

Sometimes I take readings during fermentation to determine rate of fermentation, and ADF to determine when to increase temp. Those samples can be quite full of suspended solids. So the hydrometer reading can't be relied on. I'm finding that a better method is to pull a tiny sample, which chills and settled faster, and take a refractometer reading and use a calculator to adjust for alcohol.

Suspended solids of large size fall out pretty quickly, though. I'm more interested in the effect of something that can stay in suspension after 24 hours of chilling.

Agreed. Like polyphenols... they can be filtered/centrifuged out, so they're not in "solution". I don't have the equipment to really test that. But at this point, I'm going with they "probably" have some effect.

This makes me wonder if bubbles of gas can have the opposite effect. The reason fermenting beer has a lot of suspended matter is that hundreds of CO2 bubbles are rising through the liquid and creating currents, a bit like convection currents. Is there enough gaseous CO2 (as opposed to dissolved CO2) to lower the gravity and cancel out the effect of sediment raising gravity?

This makes me wonder if bubbles of gas can have the opposite effect. The reason fermenting beer has a lot of suspended matter is that hundreds of CO2 bubbles are rising through the liquid and creating currents, a bit like convection currents. Is there enough gaseous CO2 (as opposed to dissolved CO2) to lower the gravity and cancel out the effect of sediment raising gravity?

I've always tried my best to knock the carbonation out of gravity samples for just this reason.

Yep, that's what they do. They're antipoodles: they are distributed through the volume, and do lower the AVERAGE density of the whole container load of stuff, but like regular poodles, they lift the hydro, often significantly. You can give it a good spin and detach most of them.

On this thread, just for kicks, let's try to prove our assumptions, or disprove them. So far all I am saying is that suspended solids (yeast) effect a hydrometer reading. It appears that the amount of effect is in relationship to the amount of suspended solids.

Where I'm headed with this. Is using a hydrometer really the benchmark when determining final gravity in a finishing/finished beer? Is it reliably more accurate than the average correction factor / refractometer software/spreadsheet/Apps?

I have wondered about this for a while. Couple'a thoughts:

1. I'm guessing that the density of yeast cells is about 0.8, so suspended yeast should effectively decrease the density of the solute allowing the hydrometer to sink further and give a false low reading. Instead of using dry yeast how about we use yeast recovered from the fermentor? Three samples.A. Tap water.B. Tap water plus 10 gm of yeast slurry.C. Tap water plus 100 gm of yeast slurry.

2. In my experience refractometers are student instruments at best. Using my nice expensive (I forget which model) refractometer I was unable to reproduce a single result, so I traded it to an optimist for a beer filter (which is now for sale. lol)

You can eliminate the dissolved solids concern in a finished beer by refrigerating the sample for 6-8 hours. The yeast will lay down and play nice, and you get a nice clear sample.

Note: When I worked at the brewery I had to use Plato saccharometers, and I came to love them. So now I take all my readings in degrees Plato and translate the reading to SG (because I don't think in Plato).

On our Grand Canyon trip our guide said she would look for the toungues of water in the rapids and avoid where it was churned up. “You don’t float on foam!”

She might have been right, but irrelevant to our topic, if she was looking out for water circulating between surface and bottom. The issue there is a down current, I think: a mini waterfall. Rising bubbles will lift a floating object regardless of the AVERAGE density of poolwater and poodles, as it were. They are exerting an upward force. One of the more amusing demonstrations of this somewhat counterintuitive fact was an old Mythbusters episode questioning whether a swimmer would sink in an upsurge of bubbles from an undersea release of gases, because of reduced density (they will not.) The first bench test involved, you guessed it, a hydrometer in a jar with rising bubbles. Up goes the hydro.

She might have been right, but irrelevant to our topic, if she was looking out for water circulating between surface and bottom. The issue there is a down current, I think: a mini waterfall. Rising bubbles will lift a floating object regardless of the AVERAGE density of poolwater and poodles, as it were. They are exerting an upward force. One of the more amusing demonstrations of this somewhat counterintuitive fact was an old Mythbusters episode questioning whether a swimmer would sink in an upsurge of bubbles from an undersea release of gases, because of reduced density (they will not.) The first bench test involved, you guessed it, a hydrometer in a jar with rising bubbles. Up goes the hydro.

Yes, but the principle is the same: A suspended something with less density than the liquid!

Yep. Particles and bubbles will both lift a hydrometer. A refractometer will not be affected by either unless the yeast is so dense that the effect of diffusion makes it impossible to read. The gas is expelled when you close down the cover plate.

On this thread, just for kicks, let's try to prove our assumptions, or disprove them. So far all I am saying is that suspended solids (yeast) effect a hydrometer reading. It appears that the amount of effect is in relationship to the amount of suspended solids.

Where I'm headed with this. Is using a hydrometer really the benchmark when determining final gravity in a finishing/finished beer? Is it reliably more accurate than the average correction factor / refractometer software/spreadsheet/Apps?

I have wondered about this for a while. Couple'a thoughts:

1. I'm guessing that the density of yeast cells is about 0.8, so suspended yeast should effectively decrease the density of the solute allowing the hydrometer to sink further and give a false low reading. Instead of using dry yeast how about we use yeast recovered from the fermentor? Three samples.A. Tap water.B. Tap water plus 10 gm of yeast slurry.C. Tap water plus 100 gm of yeast slurry.

2. In my experience refractometers are student instruments at best. Using my nice expensive (I forget which model) refractometer I was unable to reproduce a single result, so I traded it to an optimist for a beer filter (which is now for sale. lol)

You can eliminate the dissolved solids concern in a finished beer by refrigerating the sample for 6-8 hours. The yeast will lay down and play nice, and you get a nice clear sample.

Note: When I worked at the brewery I had to use Plato saccharometers, and I came to love them. So now I take all my readings in degrees Plato and translate the reading to SG (because I don't think in Plato).

Charlie

Couple of things, Charlie. First I missed an opportunity to do your test: Right before I read back in this thread and saw this post, I pitched today's brew -- and dumped out the rest of my jar of rinsed harvested yeast! Maybe next time. Second, were those Plato saccharometers top reading? That at least eliminates the problem of seeing through a yeasty sample if not the problem we're addressing. (BTW, one reason I'm happily going back to a refractometer is that I DO think in Plato, I used to convert sg!)

As I crack my second Siera Nevada Experimental Hop IIPA, following a.... day, I thought I would share this parting wisdom on hydrometers.(https://uploads.tapatalk-cdn.com/20180211/a6e2d91ae0127d2a0bdade938976fda2.gif)